On Monday, Good Morning America anchor Robin Roberts announced to viewers that she has been diagnosed with myelodysplastic syndrome, a blood and bone marrow disease once known as preleukemia. Roberts, who beat breast cancer five years ago, will undergo chemotherapy and then receive a bone marrow transplant.

Roberts’s sister, who is a match for the bone marrow procedure, has agreed to be the donor. Roberts said she and her doctors are confident she will beat the disease.

Roberts, 51, was diagnosed with myelodysplastic syndrome (MDS) in April, on the same day that ABC’s Good Morning America beat NBC‘s Today show in the ratings for the first time in almost 16 years. Then, a few weeks ago, during a procedure in which she was having bone marrow extracted for testing, she heard that she had landed the interview with President Obama in which he would publicly endorse gay marriage. “The combination of landing the biggest interview of my career and having a drill in my back reminds me that God only gives us what we can handle and that it helps to have a good sense of humor when we run smack into the absurdity of life,” Roberts said.

Roberts plans to stay on-air during her treatment and will miss only a few days of work here and there. In a press statement, she writes:

I’ve been living with this diagnosis for awhile and will continue to anchor GMA. I love what I do and the people with whom I do it. Along with my faith, family and friends, all of you at ABC News give me the motivation and energy to face this challenge.

What is myelodysplastic syndrome?
Myelodysplastic syndromes include a group of diseases in which the bone marrow does not make enough healthy blood cells, according to the National Cancer Institute.What causes it?
The disease is caused by poorly formed or dysfunctional blood cells. Normally, the bone marrow makes stem cells that develop into red blood cells, white blood cells or platelets. In myelodysplastic syndrome, the stem cells don’t mature properly. The immature blood cells, or “blast cells,” die in the bone marrow or soon after they enter the blood, and crowd out healthy cells in the marrow. With fewer healthy blood cells, infections, anemia and bleeding can occur.

Doctors separate myelodysplastic syndromes into two categories: myelodysplastic syndromes with no known cause and myelodysplastic syndromes caused by chemicals and radiation. The former is easier to treat.

Risk factors for myelodysplastic syndromes include:

Being male or white

Older age: most people with the disease are over age 60

Past treatment with chemotherapy or radiation: Roberts said she contracted the disease through her breast cancer treatment

Exposure to certain chemicals like tobacco smoke, pesticides and solvents

Exposure to heavy metals, like mercury or lead

How is it treated?Treatment for patients with myelodysplastic syndromes range from supportive care treatments that focus on relieving symptoms and improving quality of life to aggressive treatments designed to slow or prevent the disease from progressing.

Supportive care treatments can consist of blood transfusions, growth factor therapy to increase the number of red blood cells, and treatment with other drugs and antibiotics. Aggressive care usually involves chemotherapy or chemotherapy with a stem-cell transplant.

What is the prognosis?The prognosis for myelodysplastic syndrome depends on several factors, such as whether the disease occurred after chemotherapy or radiation, whether one or more types of blood cells are affected, the number of blast cells in the bone marrow, specific changes in the chromosomes and the age of the patient

Roberts said her doctors insist that some of the scary statistics she found online don’t apply to her since she is “younger and fitter than most people who confront the disease.”

How common is it?
Myelodysplastic syndromes are diagnosed in slightly more than 10,000 people in the U.S. each year.